Reacting to Iraq's invasion and annexation of Kuwait, two European states, the United Kingdom and France, contributed large forces and participated in land, air, and sea operations. The contributions of these states varied considerably in their composition and role. The United Kingdom deployed as many forces (45,000 personnel) as the country could manage, while France sent a significant force (15,000) that fell short of its potential. Once in Arabia, the British played a major role in coalition planning, while the fr remained operationally aloof. Finally, when it came to launch offensive operations, British forces were central to the coalition's riskiest endeavors, such as special forces raids and preparing a fake amphibious invasion, while fr forces played a credible, but less dangerous role. This article tests the ability of realism and historic institutionalism to explain these different responses to the 1990-91 Gulf Crisis. Although realism appears a priori to possess a high degree of explanatory power, a detailed process tracing analysis reveals that historical institutionalism can better account for the different outcomes observed.